This invention relates to an alkali-swellable crosslinked acrylate copolymer, methods of manufacture thereof, and a composition comprising the alkali-swellable crosslinked acrylate copolymer. The copolymer is useful to thicken compositions to provide desirable storage and flow properties.
Rheology modifiers are used to control the viscosity of a variety of consumer and commercial products, including laundry detergents and personal cleaning formulations, such as shampoo and body wash. The rheology modifier may be used to thicken a formulation to provide a more appealing viscosity and to provide desirable flow characteristics, for example to provide a consistency suitable for squeezing through an orifice. Rheology modifiers can also be used to suspend gas bubbles, encapsulated additives, or solid particles within a formulation for extended periods of time, effectively preventing settling.
Rheology modifiers can be natural or synthetic. Modified natural compounds which have been utilized in the art for many years include starch, cellulose, alginate, and protein. Synthesized polymeric thickeners include acrylic-based polymers derived from acrylic acid or acrylate esters among others. The rheology modifier may be an alkali-swellable polymer. Alkali-swellable polymers thicken upon neutralization with a base, and thus provide desirable formulation properties because they are easily processed.
The viscosity of a formulation may be enhanced by addition of a salt, such as sodium chloride, sodium sulfate, or ammonium chloride, or a polymer such as cellulose, to the formulation. Many thickeners, including salts and some polymers, provide Newtonian properties, that is, a relatively invariant viscosity across a wide range of shear rate. However Newtonian properties are not suitable for many applications because if an amount of the salt or the polymer is used to provide a viscosity at low shear rates sufficient to suspend gas bubbles, encapsulated additives, or solid particles, the formulation also has too high of a viscosity at higher shear rates, rendering it too thick to pour.
Polymers having long alkyl chains, e.g., associative thickeners, can also be used to suspend gas bubbles, encapsulated additives, or solid particles. Associative thickeners are understood to form crosslinks or other intermolecular associations between hydrophobic alkyl groups on different chains of the polymer. However associative thickeners are expensive due to the use of exotic surfactant-like monomers or chain terminators and thus can be economically undesirable. Further, in higher concentrations associative thickeners can result in coagulation when used in emulsion polymerization.
Thus there remains a need for improved materials and methods to control rheology.